1. Field of the Invention
The present invention relates to gas pressure control apparatus. More specifically, the present invention is directed to a gas control apparatus having an adjustable outlet gas pressure.
2. Description of the Prior Art
Gas control apparatus for controlling a gas pressure is well-known in the art for providing an outlet gas pressure regulated with respect to an adjustable setpoint. European Pat. No. 00 62 856 shows a gas control apparatus with a gas pressure regulator where the setpoint of the regulator can be adjusted by means of a solenoid operator, which is mounted on the pressure regulator. This pressure regulator is supplied via a throttle and an actuator solenoid valve with the gas supply pressure as available at the inlet of the gas control apparatus, and this pressure is used as auxiliary energy for the servo-pressure regulator. The regulator controls the pressure at the outlet of the gas control apparatus and for this purpose acts upon a diaphragm which with its opposite side engages a control spring. The stationary abutment of this control spring is adjusted by means of said solenoid operator therewith adjusting the setpoint of the pressure regulator. It is also known in the art to provide an electromagnetic actuator having a variable spring rate for an armature bias spring as shown in U.S. Pat. No. 4,290,040. This bias spring has a spring constant which depends on the actual position of the armature of the solenoid and which increases when the air gap between the armature and the magnetic core decreases. In order to achieve this the blade spring forming the control spring abuts against a support which changes the effective length of the spring dependent on the position of said armature. The present invention provides a gas control apparatus which works without such a special control spring with non-linear characteristic and furthermore is easier and less expensive to manufacture and to adjust.